Compressor blade and manufacture thereof



Zhmentor Qttomegs United States Patent 3,132,841 COMPRESSUR BLADE ANB MANUFACTURE Til-ERROR Stuart Wilder, In, Columbus, Ind, assignor to General Motors Uorporation, Detroit, Mich a corporation of Delaware Continuation of application Ser. No. 226,242., May 14, 1951. This application l't'iay 12, 1958, Ser. No. 734,669 6 (Iiaims. (@l. 253-'77) This application is a continuation of my application Serial No. 226,242 filed May 14, 1951, now abandoned.

My invention is directed to compressor blades and the like and to a method of fabricating the same. The invention is more particularly directed to blades and analogous parts composed principally of plastics, such as fibrous material impregnated with a thermosetting resin, and to arrangements for mounting such blades.

The presently preferred embodiment of the invention, to which Lhe succeeding detailed exposition is directed, is in rotor or stator blades for axial-flow compressors.

Such blades are ordinarily made of metal. However, plastic materials offer many advantages, among these being light weight, great mechanical strength, superior vibrationdamping characteristics, resistance to corrosion, smoothness of surface, and adaptability to mass production of typical blade forms at relatively low cost.

As compared to metal blades, plastic blades have been at a great disadvantage hitherto in that no satisfactory means for mounting them has been devised. Typically, a compressor blade is provided with an enlarged base formed for insertion in a dovetail groove in the compressor rotor or stator. The provision of such a base on a metal blade involves manufacturing ditficulties and expense, but can be done satisfactorily. Previous attempts to provide a base on a plastic blade have not been satisfactory, principally because of weakness of the blade at the root with consequent liability to fracture.

An object of the present invention is to provide a plastic blade with a base suitable for mounting on a supporting structure, while retaining the strength of the laminated plastic. A further object is to provide such a blade, and a manufacturing process therefor, adapted for low cost mass production methods.

Another object of the invention is to provide a metallic sheath for a plastic blade. Such a sheath is desirable in certain cases for increased erosion resistance. With such a sheathed blade, the erosion resistance of metal may be combined with the light weight and desirable vibration-damping characteristics of plastic.

The advantages of the invention and the preferred manner in which the stated objects are achieved will be apparent to those skilled in the art from the succeeding detailed description of preferred embodiments of the invention and the accompanying drawings, in which FIG- URE 1 is a side view of a first form of compressor blade; FIGURES 2 and 3 are sectional views thereof taken on the planes indicated in FIGURE 1; FIGURE 4 is a crosssectional view of a pile of plies of impregnated fabric before forming into a blade; FIGURE 5 is a partial sectional view of the same taken on the plane indicated in FIG- URE 4; FIGURE 6 is a cross-sectional view of a blade mold; FIGURE 7 is a partial sectional view of a blade mounted on a compressor rotor; FIGURE 8 is a longitudinal section of a blade with a metallic sheath; and FIGURE 9 is a cross-section thereof on the plane indicated in FIGURE 8.

Referring first to FIGURES 1 to 3, the compressor blade there illustrated comprises two parts, a blade proper 11 and a base or adapter 12. The blade 11 comprises an air-moving part 13 which may be of any suitable form, ordinarily a cambered airfoil with twist. The blade may 3,132,841 Patented May 12, 1964 taper in width and thickness if desired. The blade 11 also comprises a flared foot portion 14 by means of which it is attached.

The blade 11 is made of a suitably strong and refractory plastic material, preferably a plurality of plies 16 (FIG- URE 4) of glass fiber cloth impregnated with a suitable thermosetting resin. Suitable substances are known to those skilled in the plastic molding art; my invention is not concerned with the chemistry of the blades.

The plies 16 are divided and splayed out laterally at the base 14 by an insert 18 (FIGURES 2 and 5) of any suitable character which acts as a filler between the plies and creates a foot of trapezoidal cross section, as indi cated in FIGURE 2, Without a too abrupt change in direction of the fabric plies. By this arrangement, the plies which extend through the part 13 of the blade continue through the outer part of the surface of the foot 14 to the inner end surface 19 of the blade. may be a shaped piece of plastic, but is preferably a wad of material similar in character to that which forms the plies 16. The insert 13 need not be of triangular cross section in the raw state, as it may be formed to an approximately triangular cross section in the molding press in which the blade is formed and impregnated. Preferably, the plies i6 splay out at about a 30 angle at each side, which does not seriouslyweaken the laminations. The filler 18 acts to prevent wrinkling of the plies 16 at the foot of the blade.

The base 12 is preferably a metal part, as, for example, a die casting of aluminum or magnesium alley, or may be a molded plastic part. The outer contours of the base 12 may be of any suitable form for installation on a compressor rotor or stator body. As illustrated, it is formed with longitudinal ribs 24 adapted for mounting in an easily machined conventional dovetail groove in a rotor such as rotor 25 (FIGURE 7). The compressor structure is not further illustrated, as such structures are well known and further explanation thereof is unnecessary to an understanding of the invention. The internal opening 26 of the base is shaped and dimensioned to conform to the outer contours of the blade foot 14 and preferably the immediately adjacent part of the blade proper 13., The upper surface 27 of the base ordinarily coincides with the surface of the rotor or stator in which it is mounted. The under surface 28 of the base 12 is preferably coplanar with the end surface 19 of the bladewhen these two parts are assembled. The part-12 may be considered as an adapter, since it would be impracticable to machine the rotor to receive the blade foot 14 directly.

The blade is manufactured by providing a suitable mold such as that illustrated rather schematically in FIGURE 6. Such a mold may comprise an upper mold part 31 and a lower mold part 32 which, when forced together in a suitable molding press, define an internal cavity 33 of the form of the blade which is to be produced. The blade is reinforced by suitable fibrous material, which is preferably a plurality of plies 16 of glass fiber fabric, as illustrated in FIGURE 4. Some of these plies may be of less width than the width of the blade between the leading and trailing edges to accommodate the reinforcing material to the tapering section of the blade, as illustrated in FIGURE 4. The plies 16 are assembled together and the spacer element 18 is inserted at one end.

This mass of impregnated reinforcing material is placed The insert 18 3 with regard to characteristics desired in the finished product.

Likewise, no detailed description of the method of manufacture of the base fitting 12 need be presented since, by the application of known techniques of casting, forging, machining, die casting, or plastic molding, fittings of the form illustrated, or other forms that may be desired, can be produced in quantity. Particularly for large scale production, die casting is the preferred method, since it is rapid and economical and well adapted to the manufacture of parts of complex form and a very considerable degree of accuracy of dimension. It will be understood, of course, that the actual forms of the parts 11 and 12 may be of great variety, depending upon the specific installation requirements.

When the two parts 11 and 12 are completed, they are assembled by slipping the base fitting 12 over the blade into engagement with the flared foot. For convenience in handling, the two parts may be cemented together, or may be a rather tight or jammed fit. This is not essential for retention of the blade in the rotor since the flared foot provides for that, and may in some cases be undesirable, since a slight looseness of the blade in the base may be beneficial in minimizing any tendency to vibration. Preferably, the surfaces 19 of the bottom of the blade and 28 of the bottom of the base are substantially coplanar, or the surface 19 extends slightly beyond the surface 28. In any event, preferably the surface 19 is flat and rests closely against the bottom surface of the dovetail groove when the blade is in place in the rotor 25 (or stator) so that the blade is not free to move up and down in the socket in the base.

The finished blade assemblies are installed in a compressor rotor or stator in known manner by inserting them in dovetail grooves and may be retained against sliding out of the grooves by any suitable means.

FIGURES 8 and 9 illustrate a compressor blade assembly similar to that previously described except that the blade is provided with a metal sheath which preferably extends through the base member. In FIGURES 8 and 9 corresponding parts are identified by the same reference numerals as in the previously discussed figures. The blade 13, including the foot 14-, may be identical to that previously described except that the dimensions would be modified to allow for the thickness of a metallic sheath 40 which fits closely over the blade 13 and foot 14. This metallic sheath may be of any metal having desired characteristics, principally resistance to abrasion and corrosion. It may be applied in various Ways, such as, for example, by plating the plastic or spraying metal onto the plastic. Alternatively, the sheath 46 may be formed of light sheet metal by known methods of sheet metal forming, as by the use of suitably formed dies. If the form of the blade admits, the sheath 40 may be formed as a tubular member separately from the blade and slipped over the blade. Alternatively, the sheath may be a folded metal sheet open at either the leading or trailing edge of the blade and may be fitted to the blade and soldered or otherwise suitably joined together along the open edge. If a sheet metal jacket is used, it will in most cases be preferable to bond it to the plastic blade by a suitable adhesive. It is possible, and perhaps preferable, to place the metal jacket in a mold such as 31, 32 (FIGURE 6) with the laminations 16 within the jacket and then form the blade.

It will be noted that the sheath 40 includes a flaring foot portion 41- conforming to the faces, at least, of the foot 14 of the plastic part of the blade. The base 12 is formed with an internal opening 26 dimensioned to fit over the sheathed blade. I believe that in many cases it would be preferable to solder or braze the sheath 40 to the base 12, but this is not necessary. The fit between the parts 40 and 12 may be somewhat loose or the parts may be dimensioned for a jam or lock fit at assembly. If the form of the blade admits, the sheath 40 may be united with the base by soldering or the like, and the blade 13 may thereafter be inserted into the sheath.

It is believed that the advantages of the two forms of the invention disclosed above will be apparent to those skilled in the art, as well as the advantages of the methods disclosed by which these articles may be manufactured. By virtue of the invention, a compressor blade of highly desirable characteristics may be easily produced at relatively small expense in large quantities with relatively simple equipment and a minimum of skilled labor. The process is particularly adapted to produce a blade of high dimensional accuracy and good surface finish. The relatively light Weight of the blades, as. compared to metal blades, is advantageous in permitting reduction of weight of a compressor rotor on which they are mounted, and the great strength and resistance to shock of the laminated plastic makes it particularly suitable for axial-flow com pressor installations. The plastic blades are also desirable because of their vibration-damping characteristics, which greatly reduce stresses in the blades due to vibration.

It will be further apparent that the advantages of the article and process are not restricted to compressor blades. For example, the invention offers promise in the fields of aircraft propellers, particularly those of a supersonic type, and in airfoil elements of high speed aircraft and aerial missiles.

The detailed description ofthe preferred embodiments of the invention is not to be considered as restrictive, since many modifications thereof may be devised by the exercise of skill in the art within the principles of the invention.

I claim:

1. In combination, a compressor body defining one wall of a compressor air passage and having an undercut slot therein; a laminated plastic fluid-directing blade of airfoil section having a foot, the blade extending spanwise of the blade from the slot, the slot extending chordwise of the blade at the foot thereof; the foot of the blade comprising an enlarged portion extending chordwise of the blade flaring toward the bottom of the slot and comprising laminations flaring from each surface of the blade and a generally prismatic spacing member disposed between the flaring laminations in the foot and bonded thereto to maintain the said lamination in flaring relation; the foot being mounted in the slot and restrained against movement toward the body by engagement with the body at the bottom of the slot; and an adapter retaining the blade in the slot having ribs for dovetail engagement in the undercut slot and an opening elongated chordwise of the blade and tapering spanwise of the blade to conform to the foot of the blade, the foot of the blade being received in the said opening.

2. A combination as recited in claim 1 including a metallic sheath fixed on and closely enclosing the blade.

3. A combination as recited in claim 2 in which the adapter is composed of a metallic material and is bonded to the sheath.

4. In combination, a fluid-directing body comprising a blade of cambered airfoil section and a cambered foot integral therewith, the blade extending spanwise thereof from the foot andthe foot extending chordwise of the blade at one end thereof; the body being composed of a plurality of plies of high tensile strength reinforcing fabric lying generally parallel to the faces of the blade and impregnated with a rigid plastic material; the foot being elongated chordwise of the blade and being bounded by, surfaces diverging outwardly from the faces of the blade, the plies diverging outwardly in the foot substantially parallel to the said diverging surfaces, the foot including a generally prismatic spacing element disposed between the diverging plies in the foot and bonded thereto to maintain the said plies in diverging relation; and an attaching member for the body having a camber-ed internal opening elongated chordwise of the blade and tapering spanwise of the blade contoured to fit the foot 5 of the body and retained thereon by the divergence of the :foot.

5. A combination as recited in claim 4 in which the attaching member embraces the portion of the blade adjacent the foot and the opening in the attaching member is contoured to fit the said portion.

6. A fluid-directing element adapted for mounting on a body of a turbomachine having undercut slots compris ing, in combination; a laminated plastic fluid-directing blade of cambered airfoil section having a cambered foot, the blade being adapted for mounting on the body With the blade extending spanwise of the blade from the slot' References Cited in the file of this patent UNITED STATES PATENTS 1,035,364 Leblanc Aug. 13', 1912 1,175,460 Leblanc Mar. 14, 1916 2,588,570 Pitcairn Mar. 11, 1952 2,621,140 Bitterli et a1. Dec. 8, 1952 2,751,188 Rath June 19, 1956 FOREIGN PATENTS 375,059 France May 4, 1907 861,978 France Feb. 22, 1941 502,409 Great Britain Mar. 13, 1939 r 591,135 Great Britain Aug. 8, 1947 

1. IN COMBINATION, A COMPRESSOR BODY DEFINING ONE WALL OF A COMPRESSOR AIR PASSAGE AND HAVING AN UNDERCUT SLOT THEREIN; A LAMINATED PLASTIC FLUID-DIRECTING BLADE OF AIRFOIL SECTION HAVING A FOOT, THE BLADE EXTENDING SPANWISE OF THE BLADE FROM THE SLOT EXTENDING CHORDWISE OF THE BLADE AT THE FOOT THEREOF; THE FOOT OF THE BLADE COMPRISING AN ENLARGED PORTION EXTENDING CHORDWISE OF THE BLADE FLARING TOWARD THE BOTTOM OF THE SLOT AND COMPRISING LAMINATIONS FLARING FROM EACH SURFACE OF THE BLADE AND A GENERALLY PRISMATIC SPACING MEMBER DISPOSED BETWEEN THE FLARING LAMINATIONS IN THE FOOT AND BONDED THERETO 